Such measuring transducers are especially applied in Coriolis-flow measuring devices. According to the Coriolis principle, whenever, in a system, a rotating mass movement and a straight line mass movement extending at least partially perpendicular to the rotational axis superimpose, an additional force always acts on the moved mass; this force is referred to as the Coriolis force. This effect is utilized in known manner in Coriolis flow measuring devices, for example, in order to determine a mass flow of a medium flowing in a pipeline. During use, such Coriolis flow measuring devices are, as so called inline-measuring devices, inserted in a pipeline flowed through by the respective medium.
Frequently, measuring transducers are applied in Coriolis flow measuring devices having two measuring tubes connected for parallel flow, between which a medium flowing in the pipeline is divided. As a rule, during use, the two measuring tubes are excited with opposite phase relative to one another. In this way, a decoupling of the oscillatory system which has the two measuring tubes from external vibration influences is achieved. Additionally, a measuring transducer of a Coriolis flow measuring device can also have more than two measuring tubes, such as, for example, four measuring tubes connected for parallel flow. In such case, in industrial applications, the situation can occur that (at least) one of the measuring tubes of such Coriolis flow measuring devices becomes completely or partially plugged. This case arises especially when a high-viscosity medium, an inhomogeneous medium and/or a medium tending to form accretions flows in the relevant pipeline.
Such a plugging is difficult to detect, since flow is still possible through the at least one remaining, free measuring tube. Even in the case of complete plugging of one of the measuring tubes, performing a Coriolis mass flow measuring with the Coriolis flow measuring device is still possible. Especially, plugging of a measuring tube is not directly recognizable based on the determined mass flow value. It is, however, desirable to detect plugging of a measuring tube in Coriolis flow measuring devices as reliably and early as possible. This need exists especially in the case of hygienically critical applications and/or in the case of applications in which the medium conveyed in the relevant pipeline changes, and a mutual contamination should be prevented.
In the publication WO 2009/134268 A1, a flow-measuring device is described, by which deviation of a flow measuring device parameter is detectable. Such deviation of a flow measuring device-parameter can be brought about, among other things, by plugging of a measuring tube. In the case of a described method, temperature is registered at a first as well as at a second measuring tube of the flow measuring device, and a temperature gradient is ascertained therefrom. Deviation in a flow measuring device parameter is detected when the ascertained temperature gradient exceeds a limit value.